Excited-State Proton Transfer of Phenol Cyanine Picolinium Photoacid

Luís Pinto Da Silva, Ori Green, Oren Gajst, Ron Simkovitch, Doron Shabat, Joaquim C.G. Esteves Da Silva, Dan Huppert*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


Steady-state and time-resolved fluorescence techniques as well as quantum-mechanical calculations were used to study the photophysics and photochemistry of a newly synthesized photoacid - the phenol cyanine picolinium salt. We found that the nonradiative rate constant knr of the excited protonated form of the photoacid is larger than that of the excited-state proton transfer (ESPT) to the solvent, kESPT. We estimate that the quantum efficiency of the ESPT process is about 0.16. The nonradiative process is explained by a partial trans-cis isomerization reaction, which leads to the formation of a "dark" excited state that can cross to the ground state by nonadiabatic coupling. Moreover, the ESPT process is coupled to the photo-isomerization reaction, as this latter reaction enhances the photoacidity of the studied compound, as a result of photoinduced charge transfer. To prevent trans-cis isomerization of the cyanine bridge, we conducted experiments of PCyP adsorbed on cellulose in the presence of water. We found that the steady-state fluorescence intensity increased by about a factor of 50 and the lifetime of the ROH band increased by the same factor. The fluorescence intensity of the RO- band with respect to that of the ROH band was the same as in aqueous solution. This explains why inhibiting the photo-isomerization reaction by adsorbing the PCyP on cellulose does not lead to a higher ESPT rate.

Original languageEnglish
Pages (from-to)2058-2073
Number of pages16
JournalACS Omega
Issue number2
StatePublished - 28 Feb 2018


FundersFunder number
Israel Science Foundation1587/16, NORTE-01-0145-FEDER-000028


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